Is this what Duany wants for our towns? ... Poundbury village, Dorset. Photograph: Dave Penman/Rex Features

Andres Duany, the Billy Graham of American architecture, has descended upon little Britain with his 64-point list of errors to persuade us sinners away from the evils of modern architecture and urban planning of the past 50 years. Duany, once one of the most adventurous and fashionable architects in the US - have a look at his Atlantis Condominium, Florida [1980-2], a glamorous backdrop for Miami Vice - has clearly undergone a Carolingian conversion somewhere along the architectural road. He now speaks with the voice of the Prince of Wales, spreading the gospel of what is known as "new urbanism" (for which read old urbanism), a quasi-religious campaign aimed at making our towns and buildings look like biscuit-tin Poundbury, Prince Charles's model development in Dorset, or Seaside in Florida, a "traditional" American settlement for wannabe Stepford Wives designed by Duany himself.

While few of us would disagree with Duany when he complains of the British sins of sprawling edge-of-town retail parks, the insane spread of supermarkets undermining once independent market towns, the virulent rash of road signage, the flap of silly-looking winged-roofs (on top of a building at a retail park near you), the "rude" colours of so many new buildings, and the sheer lack of craft skills in much new development, he is wrong to attack postwar architecture in the UK.

Duany's message is confused because it conflates inventive contemporary architecture with the worst of modern urban planning. There is no question that we in Britain have become very bad at the latter. Why? There are many reasons, but the biggest perhaps is that local councils, which have pretty much all lost their in-house architects' departments over the past 30 years, allow themselves to be dictated to by property developers and to be bullied by, among other aggressive companies, our insatiable supermarket chains who strip trade from traditional high streets and town squares.

If our urban planning is all too often abysmal, this is not true of our architecture. Duany would have everywhere looking much the same if he could only stone modern architects to death. By his rules, we would live in prissy, regimented towns where, aesthetically at least, the clock had stopped in about 1840. Even within the rules of his own new urbanism game, however, Duany appears to have a shaky grasp of architectural and urban history. One of his rules, for example states that "civic buildings should be grand and private buildings recede into the background." Clearly, he has never been to Florence or any other Italian Renaissance city where magnificent and adventurous private palaces dominate whole streets or piazzas.

Another rule states that we should avoid too many buildings in one town by one architect. Fine, but what should we do with a town such as Vicenza where the buildings of Andrea Palladio predominate? Knock them down? And, what of the wonderful designs by John Nash and his office built between Regent's Park and Piccadilly Circus? Were those Regency wonders such a mistake?

"Avoid transparent facades" says Duany. Again, fine, but does anyone remember the days when the Financial Times was printed in a transparent, machine-like building designed by Nicholas Grimshaw in the East End of London? This was a special sight at night, and an architectural experience to relish.

Architecture is a continuum, a body of work created over hundreds and thousands of years, with a few minor revolutions absorbed into its capacious and generous body along the way. Our life would be very much poorer without the innovation and richness of much of the architecture of the past century. When Duany condemns the most adventurous modern architects - citing Richard Rogers, Frank Gehry and Zaha Hadid - he is forgetting, perhaps, that such architects have always existed in one guise or another and that there has always been room for their work. Think not just of Francesco Borromini and Guarino Guarini, masters of the Italian baroque at its most extreme, but of our very own Nicholas Hawksmoor and John Vanbrugh. Think of our great Victorian masters, whether Pugin, Butterfield, Burges and Street. Think of the Edwardians, of Lutyens and his playful, beautifully crafted country houses, let alone his breathtaking Viceroy's Palace in New Delhi. The list can be extended up to today.

Towns and cities develop. They grow. They witness not only new buildings in new styles but new types of buildings altogether, whether railway stations, department stores, distribution depots, power stations and airports. It would be tricky, and even a little potty, to attempt to design these in the style of Poundbury or Seaside.

If Duany can help us stop ruining our towns, cities and suburbs with gratuitous, mean-minded and rapacious new development, then we might call him blessed. If he wishes new urbanism thinking to be canonised, however, he should think a little harder of how and why architecture continues to develop and why some of us enjoy a City of London, for example, that is home to both some of my favourite English baroque churches - Hawksmoor's St Mary Woolnoth, Wren's St Mary Abchurch - and the Blade Runner-like Lloyds of London building by Richard Rogers. Bad modern architecture and poor new urban planning are not one and the same thing. Or, sin.